Polycarbonate resin, particularly bisphenol A polycarbonate, is an important engineering thermoplastic with many uses in construction, glazing and optical applications. Polycarbonate resin can be made by interfacial reaction or by melt transesterification. The melt transesterification technology has a significant environmental advantage over the interfacial process which uses phosgene for reaction with hydroxy compounds such as bisphenols. In addition melt process materials have lower levels of contaminants which make the very desirable for critical optical applications such as making compact disks.
Strong interest in the melt process technology is in part dependant on development of a satisfactory manufacturing process for the carbonate esters such as diphenyl carbonate.
Numerous methods are employed to synthesize diphenyl carbonate. The two current commercially viable methods to produce diphenyl carbonate are: 1) phosgenation of phenol in an interfacial process and 2) the titanium-catalyzed transesterification of dimethylcarbonate with phenol.
The conversion of carbon disulfide and phenol into tetraphenoxymethane is known. This reaction is effected by the use of a cuprous phenoxide complex, prepared insitu in an organic solvent by reaction of sodium phenoxide with cuprous chloride. Hydrolysis of tetraphenoxymethane to diphenyl carbonate is also known. A melt-based, solventless system in which carbon disulfide, cupric oxide (Cu.sub.2 O) and phenol are combined and reacted in one step without the need for preforming the reactive copper phenoxide species is also known.